In the presence of catalysts, curable organosilicone compositions undergo hydrosilation, a reaction involving the addition of a silicon-hydrogen bond across a pair of aliphatic carbon atoms linked by multiple bonds and finding widespread use in the production of silicone materials and organosilanes. Reactions of this type are catalyzed by metals, most notably platinum (Pt), rhodium (Rh), iridium (Ir), and palladium (Pd), and compounds thereof. In many instances it is desirable to initially retard or inhibit the hydrosilation reaction in the presence of all of the reactants and later initiate or "trigger" the reaction when desired. This requires the presence in the organosilicone compositions of an inhibitor material that inhibits hydrosilation at relatively low or ambient temperatures and allows the reaction to proceed normally at elevated temperatures, such compositions thus being latently curable compositions stabilized against premature gelation and generally known in the art.
Hydrosilation inhibitors fall into two general classes. One class is composed of materials that effectively inhibit hydrosilation over a wide range of temperatures and can be volatilized out of the organosilicone composition to allow hydrosilation to proceed. Examples of this class are pyridine (U.S. Pat. No. 3,188,299), acrylonitrile (U.S. Pat. No. 3,344,111), 2-ethynylisopropanol (U.S. Pat. No. 3,445,420), and perchloroethylene (U.S. Pat. No. 3,383,356). The other class of inhibitors are materials that are non-volatile; the inhibitory effect of these materials is overcome by heating, whereupon hydrosilation takes place. Examples of this latter class are organic phosphines and phosphites (U.S. Pat. No. 3,188,300), benzotriazole (U.S. Pat. No. 3,192,181), organic sulfoxides (U.S. Pat. No. 3,453,234), metallic salts (U.S. Pat. No. 3,532,649), aminofunctional siloxanes (U.S. Pat. No. 3,723,567), ethylenically unsaturated isocyanurates (U.S. Pat. No. 3,882,083), and olefinic siloxanes (U.S. Pat. Nos. 3,933,880, 3,989,666, and 3,989,667).
Prior art inhibitors often have a number of deficiencies. The volatile inhibitors have the disadvantage of requiring their removal from the composition before hydrosilation can commence. This leads to surface curing that retards complete reaction and leads to poor surface properties in the cured material such as wrinkling. The non-volatile inhibitors may have the disadvantage of requiring undesirably high temperatures and long curing times, e.g., greater than 150.degree. C. for extended periods, i.e., more than 5 minutes, to effect curing, or of requiring high concentrations of inhibitors, which thus dilute the desired silicone content of the product, in order to function effectively. Prior art inhibitors commonly are required to be present in compositions in amounts exceeding one hundred times the weight of metal hydrosilation catalyst present.